Flexural Rigidity and Shoot Reconfiguration Determine Wake Length Behind Saltmarsh Vegetation Patches

Abstract

Vegetation patches play an important role in controlling sediment deposition in shallow aquatic environments such as coastal saltmarshes and fluvial systems. However, predicting deposition around vegetation patches is difficult due to the complexity of patch morphology and their dynamic interaction with the flow. Here we incorporate a biomechanical model, parameterized using field data, within a 3‐D computational fluid dynamics model which allows prediction of individual shoot reconfiguration within patches due to flow forcing. The model predicts velocity attenuation and bed shear stresses within the wake of the patch which agree spatially with accretion patterns measured in the field using terrestrial lidar. The model is applied to sparse patches of Suaeda maritima, located in saltmarshes of coastal habitats, to explore the role of (I) shoot distribution, (II) patch geometry, (III) shoot flexural rigidity, and (IV) bulk flow velocity in determining the length of the predicted wake region. We demonstrate that for Suaeda maritima, with intermediate rigidity, the vertical shear layer over the vegetation controls the length of the predicted wake region. Consequently, reconfiguration due to flexural rigidity strongly impacts on wake length, confounding the relationship between patch height and wake length. A simplified model for predicting wake length based on shoot reconfiguration is applied to the simulation data and shows good agreement. The results demonstrate that the observed wake characteristics can be well explained by intraspecific variability in flexural rigidity, thus demonstrating the importance of biomechanical traits in determining flow‐vegetation‐sediment interactions.

Temporal Variability and Within‐Plant Heterogeneity in Blade Biomechanics Regulate Flow‐Seagrass Interactions of Zostera marina

“…As recently demonstrated in the study of wakes behind saltmarsh plants by Marjoribanks et al. (2019), intraspecific variability can play an important role in flow‐vegetation interactions. In the context of seagrass, it is unclear how flow‐seagrass interactions are affected by temporal variability and within‐plant heterogeneity of blade biomechanical traits.…”

Flow and Wake Length Downstream of Live Submerged Vegetation Patches: How Do Different Species and Patch Configurations Create Sheltering in Stressful Habitats?

“…Finally, the plants in Marjoribanks et al. (2019) were more rigid, with a flexural stiffness that varied on the order of 10 −5 to 10 −3 N m 2 , while in the proposed study, it varied between 10 −5 and 10 −6 N m 2 (Table 1).…”

“…We also considered fully submerged patches, while salt marsh vegetation can either emerge or be submerged depending on the tidal cycle. Finally, the plants in Marjoribanks et al (2019) were more rigid, with a flexural stiffness that varied on the order of 10 −5 to 10 −3 N m 2 , while in the proposed study, it varied between 10 −5 and 10 −6 N m 2 (Table 1).…”

Longitudinal dispersion affected by willow patches of low areal coverage

“…For example, patch widths as low as 1–2 m create wake flows extending up to tens of meters, so that the velocity does not fully recover between the patches (e.g. Caroppi et al, 2022; Marjoribanks et al, 2019). The uncertainty in modelling the mean velocity distributions in partly vegetated flows (e.g.…”